加速 C++ 练习 2.4

Question

我已经关注 Accelerated C++ 几个星期了，但我一直坚持练习 2.4 一段时间，最后我以为我找到了它，但在尝试给它不同的维度后我发现它没有真的不行，我真的不明白为什么

代码最初打印一条带框的消息，在这个特定的练习中，我应该将代码一次打印一个字符的空白的方式更改为一次写入所有木板

代码如下：

// [2-0, 2-4] Exercises
#include<iostream>
#include<string>

// saying what standard-library names we use
using std::cout;        using std::endl;
using std::cin;         using std::string;

int main()
{
    // asking for the name
    cout << "Please enter your first name: ";

    // reading the name
    string name;
    cin >> name;

    // building the message that we intend to write
    const string greeting = "Hello, " + name + "!";

    //  2.2 & 2.3 asking for inpadY
    cout << "Please enter the number of padY (Vertical padding): ";

    // 2.2 & 2.3 reading the inpadY
    int inpadY;
    cin >> inpadY;

    //  2.2 & 2.3 asking for inpadX
    cout << "Please enter the number of padX (Horizontal padding): ";

    // 2.2 & 2.3 reading the inpadX
    int inpadX;
    cin >> inpadX;

    // the number of planks surrounding the greeting
    // 2.2 & 2.3 added inpadY as the number of planks;
    const int padY = inpadY;

    // 2.2 & 2.3 added inpadX
    const int padX = inpadX;

    // 2.4 pad size
    const int pad = inpadX + inpadY;

    // the number of rows and columns to write
    const int rows = padY * 2 + 3;
    const string::size_type cols = greeting.size() + padX * 2 + 2;

    // 2.4 creating a padding string left and right and top and bottom
    const string LeftRightPad(padY, ' ');
    const string TopBottomPad(cols - 2, ' ');

    // write a blank line to separate the output and the input
    cout << endl;

    // write rows rows of output
    // invariant: we have written r rows so far
    for (int r = 0; r != rows; ++r) {

        string::size_type c = 0;

        // invariant: we have written c characters so far in the current row
        while (c != cols) {

            // is it time to write the greeting?
            if (r == padY + 1 && c == padX + 1)
            {
                cout << greeting;
                c += greeting.size();
            } else {

                // are we on the border?
                if (r == 0 || r == rows - 1 ||
                    c == 0 || c == cols - 1)
                    {cout << "*";
                    ++c;}
                else
                    // 2.4 typing out the spaces at once
                    {cout << LeftRightPad;
                    c += LeftRightPad.size();}
            }
        }

        cout << endl;
    }

    return 0;
}

编辑为具有输入和输出

Please enter your first name: Estrogen
Please enter the number of padY (Vertical padding): 2
Please enter the number of padX (Horizontal padding): 2

**********************
*                    *
*                    *
*  Hello, Estrogen!  *
*                    *
*                    *
**********************

Process returned 0 (0x0)   execution time : 3.281 s
Press any key to continue.

Please enter your first name: Estrogen
Please enter the number of padY (Vertical padding): 2
Please enter the number of padX (Horizontal padding): 5

****************************
*                          *
*                          *
*                          *
*                          *
*                          *
****************************

Process returned 0 (0x0)   execution time : 5.098 s
Press any key to continue.

Please enter your first name: Estrogen
Please enter the number of padY (Vertical padding): 3
Please enter the number of padX (Horizontal padding): 2

**********************
*
*
*
*
*
*
*
**********************

Process returned 0 (0x0)   execution time : 4.333 s
Press any key to continue.

更新：我重写了代码，输出是星号的无限循环这里是新代码

#include<iostream>
#include<string>

using std::string;      using std::endl;
using std::cout;        using std::cin;

int main()
{
   cout << "Please enter your first name: ";

   string name;
   cin >> name;

   const string message = "Hello, " + name + "!";

   cout << "Enter the length: ";

   int length;
   cin >> length;

   cout << "Enter the height: ";

   int height;
   cin >> height;

   const int rows = height * 2 + 3;
   const string::size_type cols = message.size() + length * 2 + 2;

   const string TopBottom(cols, '*');
   const string Blank(cols - 2, ' ');
   const string messageblank(cols - 3 - message.size(), ' ');

   cout << endl;


    for (int r = 0; r != rows; ++r) {

        string::size_type c = 0;
        while (c != cols) {

                if ( r == height + 1 && c == length + 1)
                {
                    cout << messageblank << message << messageblank;
                    c += Blank.size();
                } else
                if (r == 0 && c == 0 || r == rows - 1 && c == cols -1)
                {
                    cout << TopBottom;
                    c += TopBottom.size();

                } else
                if ( r != 0 && c == 0 || r != rows -1 && c == cols - 1)
                {
                    cout << "*";
                    ++c;
                } else
                    cout << Blank;
                    c += Blank.size();
        }

    cout << endl;
    }


    return 0;
}

先谢谢大家的帮助

Answer 1

除非代码应该这样写，否则我会建议另一种逐行的方法：

print_frame_row(cols);
for (int i = 0; i < padY; ++i)
    print_v_padding(cols);

print_greeting(padX, greeting);
for (int i = 0; i < padY; ++i)
    print_v_padding(cols);

print_frame_row(cols);

哪里

void print_frame_row(int cols)
{
    std::cout << std::string(cols, '*') << '\n';
}

void print_v_padding(int cols)
{
    const std::string h_padding(cols - 2, ' ');
    std::cout << '*' << h_padding << "*\n";
}

void print_greeting(int padX, const std::string &msg)
{
    const std::string h_padding(padX, ' ');
    std::cout << '*' << h_padding << msg << h_padding << "*\n";
}

这样您的逻辑就更简单了，不必担心计算列数或决定何时写入每个字符。

Answer 2

好的，所以我花了 3 天时间，但我终于弄明白了这是工作代码

#include<iostream>
#include<string>

using std::string;      using std::endl;
using std::cout;        using std::cin;

int main()
{
   cout << "Please enter your first name: ";

   string name;
   cin >> name;

   cout << "Enter the length: ";

   int length;
   cin >> length;

   cout << "Enter the height: ";

   int height;
   cin >> height;

   const string message = "Hello, " + name + "!";

   const int rows = height * 2 + 3;
   const string::size_type cols = message.size() + length * 2 + 2;

   const string TopBottom(cols, '*');
   const string Blank(cols - 2, ' ');
   const string messageblank(length, ' ');

   cout << endl;

   for (int r = 0; r != rows; ++r) {

        string::size_type c = 0;
        while (c != cols) {

                if ( r == height + 1 && c == 0)
                {
                    cout << "*" << messageblank << message << messageblank << "*";
                    c += TopBottom.size();

                } else
                if (r == 0 && c == 0 || r == rows - 1 && c == 0)
                {
                    cout << TopBottom;
                    c += TopBottom.size();

                } else
                if ( c == 0 && r != 0 || c == 0 && r != rows - 1)
                {
                    cout << "*" << Blank << "*";
                    c += TopBottom.size();

                }
        }


    cout << endl;
    }

    return 0;
}

加速 C++ 练习 2.4

Accelerated C++ Exercise 2.4

c++

accelerated-c++